1. Field
Embodiments described in the present specification relate to a semiconductor memory device and a memory system.
2. Description of the Related Art
In recent years, an LSI element included in a semiconductor memory device has become increasingly shrunk as a level of integration of the semiconductor memory device has risen. Shrinking of this LSI element requires not only simply that line width be narrowed, but also requires improvement of dimensional accuracy or positional accuracy of a circuit pattern. Proposed as a technology for overcoming such a problem is ReRAM (Resistive RAM) having a variable resistance element that has reversibly changeable resistance value. Moreover, in this ReRAM, a structure where the variable resistance element is provided between a side surface of a word line extending parallel to a substrate and a side surface of a bit line extending perpendicularly to the substrate has made possible an even higher degree of integration of a memory cell array.
However, characteristics of the variable resistance element sometimes change according to the number of times that its resistance value has been changed (the number of times of executions of a write/erase operation).